1. Field of the Invention
This invention relates to power supplies for intermittently energizing a gaseous discharge tube, and more particularly, to the trigger pulse generator circuits of strobe power supplies.
2. Description of the Prior Art
Trigger pulse generators for prior art strobe lighting systems typically generate individual, spaced apart trigger pulses which initiate periodic optical output pulses from a strobe flash bulb. Another form of prior art strobe lighting device includes a trigger pulse generator which generates closely spaced, paired trigger pulses which some manufacturers refer to as a double flash output.
U.S. Pat. No. 4,013,921 (Corthell) discloses a strobe power supply having a trigger pulse generator which generates closely spaced, paired trigger output pulses for generating a double flash output. The Corthell circuit utilizes an integrated circuit square wave generator 26, the output of which is transmitted through a capacitor differentiator to produce a pulse in response to both the leading and trailing edges of each square wave output pulse. The first or positive going differentiator pulse is coupled to the gate of one SCR which generates a trigger pulse while the second or negative going differentiator pulse is coupled to the gate of a second SCR which generates a trigger pulse synchronized with the trailing edge of each square wave output pulse. The Corthell trigger circuit is unable to generate anything but closely spaced, paired trigger output pulses.
U.S. Pat. No. 4,321,507 (Bosnak) discloses another double flash strobe power supply circuit which includes an integrated circuit square wave timer. The square wave output of the timer is transmitted through a capacitor differentiator which generates a positive going pulse at the leading edge of each square wave and a negative going pulse at the trailing edge of each square wave. Closely, spaced, paired positive and negative going pulses from the capacitive differentiator are coupled to the gate of a triac which generates closely spaced, paired trigger pulses synchronized with the leading and trailing edges of each square wave generated by the timer circuit. The Bosnak circuit is thus able to generate a double flash output where each strobe lamp flash is synchronized with the leading and trailing edges of each square wave generated by the trigger pulse genertor timing device.
In another prior art device identified as the Tomar MICROSTROBE, the trigger pulse generator takes the form of a sidac-actuated relaxation oscillator including a series connected resistor and capacitor where the capacitor also serves as the trigger capacitor. A voltage controlled switch in the form of a sidac periodically assumes a short circuit condition when the trigger capacitor voltage reaches the sidac breakover voltage and generates a trigger pulse. With this prior art trigger pulse generator circuit, the frequency of the single flash output pulses is fixed.